A visceral emotional and high-stakes portrayal of life in a British prison; Mark Cobden (Sean Bean) is consumed by guilt after accidentally killing an innocent man. Accepting his four year sentence and separated from his family he meets Eric McNally (Stephen Graham) a caring prison officer doing his best to protect those in his charge. However when one of the most dangerous inmates identifies his weakness Eric faces an impossible choice; between his principles and his family. A story of guilt and forgiveness punishment and penitence both Eric and Mark are trapped by their pasts and unsure of their futures.